Heat exchanger



FIG. 1 is a perspective view of a heat exchanger showing our new design;

FIG. 2 is a top plan view of the design of FIG. 1;

FIG. 3 is a bottom plan view of the design of FIG. 1;

FIG. 4 is a rear elevation view of the design of FIG. 1;

FIG. 5 is a front elevation view of the design of FIG. 1;

FIG. 6 is a first side elevation view of the design of FIG. 1; and,

FIG. 7 is a second side elevation view of the design of FIG. 1. 

CLAIM The ornamental design for a heat exchanger, as shown and described. 